This application claims the benefit of co-pending German Patent Application No. 100 34 748.7 entitled xe2x80x9cLxc3x6sbares Verbindungselement fxc3xcr ein Fahrzeug, mit einem Schraubteil und einem Stxc3xctzringxe2x80x9d, filed on Jul. 7, 2000.
The present invention generally relates to a detachable fastener assembly for a wheel of a vehicle. More particularly, the present invention relates to a fastener assembly which includes a screw element including a threaded portion and a supporting ring being rotatably connected to the screw element.
Fastener assemblies including a screw element and a supporting ring are used to mount wheels to a hub of an axle of a vehicle. The screw element usually is a wheel bolt. However, it may also be a wheel nut also being associates with a supporting ring. In most cases, the supporting ring is captively connected to the screw element to facilitate assembly. The assembly is designed in a way that the supporting ring may not only be rotated with respect to the screw element, but the axes may also be dislocated with respect to one another in a radial direction within a predetermined play. However, this dislocation only takes place within a small region, as it, for example, makes sense to compensate dividing errors of the opening of the wheel rim and/or of the hub.
A detachable fastener assembly in the form of a wheel bolt is known from European patent application No. 0 836 016 A2. The wheel bolt includes a head and a shank including a threaded portion. The head of the wheel bolt at its side facing a supporting ring includes a supporting surface to transmit an axial force to the supporting ring. The supporting surface is designed as a plane surface. The supporting ring also includes a plane counter supporting surface being associated therewith. At its other side facing the vehicle, the supporting ring includes a non-planar bearing surface to transmit the axial force to the wheel of the vehicle. The bearing surface has a truncated cone design or a spherical design. The supporting ring is rotatably and captively connected to the wheel bolt by a calked surface. Usually, four calked surfaces are spaced apart over the circumference. The supporting ring is to be connected to the wheel bolt by the calked surface, and in a way that it may be turned with respect to the shank of the wheel bolt and that there is few friction between the supporting ring and the head of the screw when the wheels is affixed. The supporting ring may be made of a light metal alloy, whereas the wheel bolt is made of steel. In combination with the wheel of the vehicle being made of magnesium, an occurrence of contact corrosion between the supporting ring and the wheel of the vehicle is prevented. It may make sense to design the fastener assembly in a way that there only is few friction between the supporting ring and the screw head when the wheel is affixed. However, this low friction is disadvantageous with respect to unintentional loosening of the wheel bolts. With such known fastener assemblies, there is the special danger of unintentional loosening in case of transverse loads. This danger is especially important if one takes into account increasing engine power and vehicle weight. Consequently, the fastener assembly is subjected to substantial transverse loads during acceleration and braking. Additionally, there is the danger of such known fastener assemblies setting, especially due to unpreventable vibrations and oscillations prevailing at the vehicle. Thus, the axial force is reduced. In case of respective transverse loads, this leads to an evermore increased tendency of the known faster assembly to unintentionally loosen.
On the other hand, screws in which the supporting surface below the head has a special design to reduce the danger of unintentional loosening in case of loads are known. The supporting surface below the head includes a tooth arrangement including wedge shaped teeth. The tooth arrangement has a design in a way that the screw may be tightened comparatively easily due to slightly inclined surfaces of the tooth arrangement sliding over a component, while the teeth dig in the material of the component to be affixed after the tightening process has been finished and under prevailing load conditions. Consequently, this causes increased resistance which has to be overcome during loosening and unscrewing of the screw. The tooth arrangement desires a sliding movement of the supporting surface on the component when the screw is being tightened. On the other hand, during loosening and unscrewing, conditions requiring an increased loosening moment are desired to overcome a form-fit. The combination of the material of the screw and of the component has to be coordinated. It is to be understood that only the known screw includes a tooth arrangement, whereas the component has a plane or a flat supporting surface. In this way, unintentional loosening of the screw is usually prevented due to an increase of the friction between the supporting surface of the head of the screw and the respective counter surface of the component. On the other hand, intentional loosening of the screw by applying a respectively increased loosening moment is possible. A multiple use of such a known screw is limited.
Lock washer assemblies which are used in combination with a screw are known from German patent document No. 24 13 760, U.S. Pat. No. 3,263,727 and European patent document No. 0 131 556. The lock washer assemblies include two superposing washers which may have an identical design and which are supported on one another in a point-symmetric way. The two washers are located between the plane supporting surface being located at the head of the screw and the plane supporting surface being located at the component. The two washers at their outwardly facing surfaces, meaning the supporting surface facing the head, on the one hand, and the supporting surface facing the component, and the other hand, include a tooth arrangement which increases friction. The tooth arrangement includes a number of radial ribs or the like. The two washers at their sides facing one another each include a tooth arrangement including wedge shaped teeth. The tooth arrangements include inclined plane surface portions and possibly additional surface portions which are directed perpendicular with respect to the axis of the washer assembly and of the screw, respectively. The inclined surface portions are arranged at different inclination angles in the direction of the circumference to realize form-fit between the two washers when the screw is being tightened. When the screw is being rotated in the loosening direction, the respective wedge surfaces slide on one another in a way of an inclined plane to increase the axial force. During loosening or untightening of the connection, the increased axial force has to be overcome. The manufacture of such known washer assemblies is expensive, and the number of elements used for the connection is increased. In addition to the screw, the two washers have to be handled and, more importantly, they have to be mounted in the correct orientation. The washers are separate components which are not captive. The use of separate washers in combination with detachable screws has the further disadvantage of the number of parting lines and setting lines between the respective elements of the connection being increased. The greater the number of these lines is, the higher is the setting value of the connection caused thereby which results in a dangerous reduction of the axial force. This is especially the case when the elements used for the connection have a certain surface design, for example a coating reducing corrosion or the like, and when these elements are subjected to increased temperatures during operation. It is to be understood that such known separate washer assemblies are not suitable as detachable fastener assemblies for the attachment of the wheel of a vehicle since the respective bearing surface at the wheel rim has a conical or spherical shape, meaning a non-planar bearing surface. Due to the fact that such wheel bolts or wheel nuts are loosened and tightened very often, there are special conditions in which the washer assembly cannot be applied.
Furthermore, it has to be taken into account that the use of wheel bolts or wheel nuts as detachable fastening elements for wheels of a vehicle takes place under conditions which promote corrosion. To improve corrosion properties, it is known to apply a coating on the wheel bolts and on the supporting rings. For example, the coating is a zinc lamella coating including plastic components and metal particles, especially zinc, aluminum and the like, which are contained therein. Such coatings improve corrosion properties, but, at the same time, setting properties deteriorate. The respective setting values occurring at such connecting elements increase with an increasing number of separating lines being located between the elements and with an increase of the thickness of the coating.
The present invention relates to detachable fastener assembly for a wheel of a vehicle. The fastener assembly includes a screw element including a threaded portion, a first supporting surface and a number of first wedge shaped teeth being located at the supporting surface. A supporting ring is rotatably connected to the screw element. The first supporting surface is designed and arranged to transmit an axial force to the supporting ring. The supporting ring includes a second supporting surface, a non-planar bearing surface being designed to transmit an axial force onto a wheel of a vehicle in the mounted position and a number of second wedge shaped teeth being associated with the first wedge shaped teeth. The first wedge shaped teeth are located at the first supporting surface to face the supporting ring and the second wedge shaped teeth are located at the second supporting surface to face the screw element. The first and second wedge shaped teeth are designed and arranged in a way to realize positive engagement between the screw element and the supporting ring when the fastener assembly is being tightened and to make the first and second wedge shaped teeth slide on one another and to press the screw element and the supporting ring apart under an increase of the axial force when the fastener assembly is being loosened.
With the novel fastener assembly, the known detachable fastener assemblies in the form of wheel bolts and wheel nuts including a supporting ring are improved without increasing the number of elements. The application of a tooth arrangement including wedge shaped teeth results in an increase of the axial force in case of unintentional loosening. Consequently, the novel arrangement counteracts unintentional loosening in case of increased loads. In known fastening assemblies, transverse forces subjecting the elements of the fastening assembly in case of respective loads usually lead to unintentional loosening of the screw element. In the novel fastening assembly, the loosening movement is terminated by the sliding movement of the two tooth arrangement on one another, and a further decrease of the preloading force is prevented. Due to this unpreventable loosening movement in case of transverse loads, an axial movement and a tangential movement of the screw element with respect to the supporting ring takes place in the novel fastening assembly in combination with the tooth arrangements. As a result, the loss of preloading forces is advantageously compensated. This especially applies when the preloading force has already been reduced due to unpreventable setting effects, and when the portion of the transverse force being transmittable between the connected elements (namely the wheel rim and the hub) due to friction, has been reduced. It is a similar case when the wheel connection has not been tightened with the prescribed torque during inappropriate maintenance service and the preloading force level necessary for a secure connection has not been reached. Insofar, the present invention also improves driving safety.
With the novel fastener assembly, it is possible to securely fix the wheel to a motor vehicle, even in case of great engine power, great vehicle weight and extremely loaded wheels of the vehicle. The detachable fastener assembly only includes a small number of components, it may be assembled simply and safely and it may be used several times.
Due to the arrangement of the first tooth arrangement at the screw element, meaning for example the wheel bolt or the wheel nut, and of the second tooth arrangement at the supporting ring, the number of elements used in the fastener assembly is not increased compared to the prior art. The number of setting lines does not differ from the one of a known fastener assembly including a wheel bolt and a supporting ring. Consequently, increased setting values do not have to be taken into account when the elements are protected against corrosion, for example by a zinc lamella coating. The novel fastener assembly overcompensates the disadvantage resulting from a zinc lamella coating.
The supporting ring may be captively connected to the wheel bolt or the wheel nut. To be captively connected means that the supporting ring may not unintentionally be detached from the wheel bolt or the wheel nut. In this way, one attains an assembly unit which is easy to handle and which may be used and operated as one complete unit. The novel fastener assembly may for example be handled by robots, especially during first assembly.
Another advantage of the novel fastener assembly is the fact that an increased clamping length is maintained due to the use of the supporting ring. The wheel bolt has an elastic design which has the positive effect of maintaining the axial force, especially in case of setting effects occurring in the fastener assembly. This effect may be further supported by choosing a more elastic materiel for the supporting ring compared to the materiel of the screw element or by designing the supporting ring as a hollow body. It may be advantageous to design the form surfaces of the tooth arrangement below the head of the screw element to be conical with respect to the axis of the screw element and to attain a disc-spring-like effect by a respective design of the counter surface.
In case of a plane design of the tooth arrangement, the novel fastener assembly allows for a compensation of tolerances. The supporting rings may adapt to the respective conditions prevailing at the counter surface being located at the wheel. Great preloading forces may be applied and comparatively great remaining preloading forces occur during operation. The clamping forces may be transmitted to the wheel rim in more uniform way.
Another advantage of the novel fastener assembly is the fact that the loosening and untightening moments have a reduced value and a reduced spreading compared to usually occurring extremely great loosening and untightening moments being caused by corrosion effects. In the novel fastener assembly, the loosening moment being required to loosen the screw element may be adjusted to be less than the frictional moment between the supporting ring and the wheel of the vehicle. This effect is attained in a simple way and with great exactness by a respective design of the surfaces, a respective choice of materials and the like. This is especially advantageous in case of having to change a wheel due to an accident or a breakdown of the vehicle. Usually, such a change of tires has to be realized by the driver by means of simple tools which are carried on the vehicle.
The first and second tooth arrangements including wedge shaped teeth are designed and arranged to be asymmetric in a circumferential direction. Each tooth includes two form surfaces being inclined in a circumferential direction. The form surfaces contacting one another in the tightening direction are arranged at a comparatively great average tangent angle to attain the desired form-fit. The form surfaces contacting one another in the loosening direction are arranged at a comparatively small average tangent angle to achieve the desired sliding movement. It is to be understood that the tangent anglesxe2x80x94as seen from the decisive directionxe2x80x94may change locally in case the form surfaces are designed as non-planar surfaces. This means that the term xe2x80x9cnon-planar surfacesxe2x80x9d has to be understood throughout this application in a special way. Cutting the fastener assembly cylindrically around its axis and putting the image into a planar area shows a straight cutting line generated by the cylindrical cutting area and the form surfaces, especially the form surfaces acting in the loosening direction, even in case the form surfaces are designed as threadlike non-planar surfaces. However, if there is a xe2x80x9cnon-planar surfacexe2x80x9d in the sense of this application, a non-straight line, i.e. a curved or an angled line, appears as a cutting line in the circumferential direction, which at the same time means that the tangent angle in the circumferential direction is not constant.
The form surfaces of the tooth arrangements may have different designs. The form surfaces may not only have a plane design, but also a non-planar design, for example a ball-like, involute or the like design. The tooth arrangements including wedge shaped teeth do not have to extend over the entity of the surfaces at the screw element and at the supporting ring, but they may also be designed to only cover a portion of these surfaces. It is also possible to design radial, plane surface portions. It is important that the tooth arrangements have different properties depending on the respective sense of rotation. It is desired to attain a form-fit or a positive engagement in the tightening sense of rotation. In a direction opposite the tightening direction, meaning the loosening direction, the effect of an inclined plane is to be used to prevent a decrease of the axial force.
Furthermore, it is desired that the respective effective tangent angle of the second form surfaces contacting one another in a loosening sense of rotation is more than a helix angle of the threaded portion of the screw element. This is at least desired for the first portion of the tooth arrangements in the loosening direction.
The second form surfaces of the screw element and/or the supporting ring contacting one another to attain the sliding movement in the loosening sense of rotation may be designed to be at least partially non-planar surfaces. The form surfaces include different tangent angles, but not one constant tangent angle. The tangent angle in the loosening sense of rotation starts with a small tangent angle however being larger than the helix angle of the threaded portion. Then, in circumferential direction, the tangent angle becomes greater. The tangent angle may become very great, similar up to a size like the acting tangent angle in the tightening sense of rotation. This design prevents the slide of the wedge shaped teeth to one another and the corresponding wear. Thus, the fastener assembly may be used several times again and again. In this case, one is capable of influencing the loosening moment during intentional unscrewing and during unintentional loosening by the design of these form surfaces and their geometry in a circumferential direction, due to settling effects also.
The supporting ring may connected to the screw element to be captive but movable. Movability relates to a possible dislocation occurring between the screw element and the supporting ring to allow for a compensation of dividing errors. There are a number of possibilities of achieving the captive connection. A simple possibility is to first push the supporting ring over the shank of the screw element and to then produce the thread at the threaded portion by rolling. The outer diameter of the thread will be more than the inner diameter of the bore of the supporting ring. It is also possible to later produce a securing channel, a protrusion or the like at the shank of the screw element by rolling. Another exemplary possibility is to calk the supporting ring.
The non-planar bearing surface of the supporting ring which serves to transmit the axial force to the wheel of the vehicle may be designed to have an increased frictional moment. This design desires to provide a greater frictional moment between the wheel of the vehicle and the supporting ring than between the supporting ring and the screw element to attain a movement in the region of the tooth arrangements due to unintentional loosening under load and to use the positive reclamping effects. This at least applies to the beginning portion in which unintentional loosening takes place under the effects of transverse forces. The friction between the first supporting surface of the screw element and the supporting ring may be made smaller than the friction and the corresponding moment respectively between the supporting ring and the wheel of the vehicle by designing the surfaces more smooth or by the aid of grease.
There are a number of possibilities of realizing the above-described design. It is possible that the non-planar bearing surface of the supporting ring includes a number of ribs, elongated protrusions or the like to increase friction. A respective design of the surface of the wheel of the vehicle with which the non-planar bearing surface gets in contact may also make sense. Another exemplary possibility is to provide the non-planar bearing surface of the supporting ring with a coating increasing friction to attain increased friction in the system. For example, the surface may also be abrasive-blast. Any arrangement being suitable to increase friction at this place may be used.
The supporting ring includes a bore or an opening independent from its use in combination with a wheel bolt or with a wheel nut. In all cases, the supporting ring may be designed as a hollow body and/or to include a continuous expansion channel at its outer circumference to increase its elasticity. In this way, the supporting ring is designed as an elastic, resilient body which supports the chosen great clamping length of the screw element.
The supporting ring and the screw element may be made of different materials or of the same materiel having different stability. This design desires to have an influence on elasticity, to control surface pressure, to improve corrosion properties and to improve overall function of the novel fastener assembly.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and the detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention, as defined by the claims.